Stereophonic sound collecting device



Dec. 25, 1962 D. KLEIS ET AL 3,070,658

STEREOPHONIC SOUND COLLECTING DEVICE Filed July so, 1957 INVENTOR DERK KLEIS J-OHANNES SNOEK BY v I AGEN Patented Dec. 25, 1962 3,070,653 STEREUHIONIC SOUND COLLEQTING DEVICE Derir Kieis and Johannes Snoek, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Deiaware Filed .luty 30, 1957, Ser. No. 6753968 Claims priority, application Germany Aug. 31, 1956 4 tilaims. (Cl. 179-1) The present invention relates to stereophonic sound collecting devices.

With stereophonic recording it is known to use an acoustical obstacle provided on either side with a microphone. Analogous to the human head such an obstacle is usually shaped in the form of a ball and therefore the obstacle is often termed artificial head. The spherical shape of the artificial head is found to be of no essential importance. The determinative factor is the screening effect, i.e. the detour about the artificial head. Thus, the shape of the artificial head need not be restricted to the spherical form, if it serves as a sound screening surface between at least two microphones. The term sound screening surface is to be understood to mean an obstacle between two microphones, so that intensityand time-differences are introduced into the sound captured by the microphones from a sound source arranged in an asymmetrical manner relative to the microphones, the microphone arrangement being thus suitable for stereop'honic recording.

In accordance with the present invention, the stereophonic sound collecting device comprises a body having the sound screening surface constituted by a fiat plate and animaginary line of connection between two stereophonically associated microphones at right angles to the surface of the plate. Thus a very simple form of the artificial head can be obtained.

With the use of an artificial head shaped in a spherical form it is known, with respect to the desired angular aperture of the artificial head to choose the dimensions thereof accordingly. The term angular aperture is to be understood to mean herein that part of the recording space which is governed by the artificial head and which is represented linearly between the stereophonically associated loudspeakers during the reproduction, the sound image filling out the space between these loudspeakers wholly or partly. In order to fulfill the latter condition, while the same distance between the loudspeakers is main tained, and to satisfy the requirements of the recording operation (larger or smaller space angle), it is efficient, as stated hereinbefore for a spherical artificial head, to vary the angular aperture. This is possible with the device according to the invention, since the dimensions of the sound screening surface of the flat plate are variable.

This variation may be realized in a simple manner by providing the sound screening plate with a plate-shaped or a disc-shaped part which is slidable or rotatable in the plane of the plate.

The axis of rotation of the disc-shaped part may coincide with the imaginary line of connection between two stereophonically associated microphones, so that the microphones can stay at their places with a variation of the sound screening surface.

The invention is not restricted to the aforesaid cases, and combinations thereof are, of course, possible.

The microphones may be arranged in a manner such that they are displaceable in the direction of their junction line or at right angles thereto.

In order that the invention may be readily carried into effect, it will now be described more fully with reference to the accompanying drawing, wherein:

FIG. 1 is a side view of the sound screening plate of the present invention, provided with a rotatable part, which consists of parts of different circular surfaces;

FIG. 2 is a side view of the sound screening plate of the present invention having a rotatable part constructed from parts of different elliptical surfaces; and

FIG. 3 is a side view of the sound screening plate of the present invention having a rotatable part consisting of a body, the periphery of which is bounded by part of a spiral.

Referring to FIG. 1, reference numeral 1 designates the stationary part of the sound screening plate, in the plane of which a flat part is rotatable about the axis 2. This part consists of two semi-circular surfaces 3 and 4 with different radii. On either side of the plate 1 provision is made of a microphone 5, of which only the one shown in the drawing in front of the plate is indicated in the figures. In the position shown the angular aperture of the two stereophonically associated microphones 5 will be determined by a point of the periphery of part 4 and will have a high value. In the position indicated in broken lines, obtained by turning the plate through the sound screening surface is enlarged, so that the angular aperture is determined by a point of the periphery of part 3, and has a small value. The stationary part 1 has such a size relative to the rotatable part that the detour for the sound to be made is so large that it does not contribute to the stereophonic effect.

In FIG. 2 the stationary part of the plate is omitted and the rotatable part consists of two semi-elliptical surfaces 6 and 7 with diiferet axes, this part being rotatable about an axis 8. It is assumed that the imaginary line of connection of the two stereophonically associated microphones coincides with the axis of rotation 8. If the surface 7 serves effectively as that part of the sound screening plate which contributes to stereophonic hearing, the angular aperture of the microphones is adjusted to its higher value. After a rotation through 180, the other conditions being the same, the angular aperture is determined by a point of the periphery of part 6, so that it is adjusted to its lower value.

In FIG. 3, from which the stationary part of the plate is omitted, the fiat surface is bounded by part of a spiral. By turning the plate about the axis Iii, the angular aperture can be varied continuously within comparatively wide limits.

As a rule, the device will be directed to the sound source along the lines II, 11-11 and IIIIII in the manner indicated by the corresponding arrows in the figures.

Although the invention is described with reference to a device comprising two stereophonically associated microphones, it will be obvious that the invention is not restricted thereto and that each of the said microphones may be replaced by a column of microphones, the longitudinal axis of the column being then parallel to the surface of the plate and at rightangles to the lines I-I, IIII and III-III. Under certain circumstances, it may be advantageous to utilize, during the recording operation, the known form of the characteristic curve of the direction-sensitivity of the column. Even with the use of a single set of microphones it may sometimes be advantageous to use direction-sensitive microphones, for example those having a cardioid characteristic curve.

While the invention has been described by means of specific examples and in specific embodiments, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. Stereophonic sound collecting apparatus comprising at least two microphones spatially positioned, an imaginary line of connection between said microphones, and a sound screening surface interposed between said microphones at substantially right angles to said imaginary line connecting said microphones, said surface including a flat 3 plate which is stationary and a movable flat plate with a substantially semi-circular edge portion which is rotatable in a juxtaposed parallel plane of said stationary plate to thereby vary the overall size of said screening surface.

2. Sterecphonic sound collecting apparatus comprising at least two microphones spatially positioned, an imaginary line of connection between said microphones, and a sound screening surface interposed between said microphones at substantially right angles to said imaginary line connecting said microphones, said surface including a plate which is stationary and a movable plate with a substantially semicircular edge portion which is rotatable in a juxtaposed parallel plane of said stationary plate to thereby vary the overall size of said screening surface, said movable plate being rotatably connected to said stationary plate and having an axis of rotation substantially coincident with said imaginary line.

3. Stereophonic sound collecting apparatus comprising at least two microphones spatially positioned, an imaginary line of connection between said microphones, and a sound screening surface interposed between said microphones at substantially right angles to said imaginary line connecting said microphones, said surface including a fiat aomass plate which is stationary and a movable flat plate which is rotatable in a juxtaposed parallel plane of said stationary plate to thereby vary the overall size of said screening surface, said rotatable fiat plate comprising two curved segments of different sizes, said segments being integral.

4. Stereoplionic sound collecting apparatus comprising at least two microphones spatially positioned, an imaginary line of connection between said microphones, and a sound screening surface interposed between said microphones at substantially right angles to said imaginary line connecting said microphones, said surface including a flat plate which is stationary and a movable fiat plate which is rotatable in a juxtaposed parallel plane of said stationary plate to thereby vary the overall size of said screening surface, said rotatable fiat plate having a substantially curved configuration.

References Cited in the file of this patent UNITED STATES PATENTS 2,093,540 Blumlein Sept. 21, 1937 2,520,798 De Boer Aug. 29, 1950 2,563,010 De Boer et a1 Aug. 7, 1951 2,791,628 Edmondson May 7, 1957 

